I have run into a small snag in using alphas. It seems the renderer insists on rendering the hidden geometry (the ‘backside’ of an object), which means specular colors show up in unwanted places. Here are two pictures to examplify the issue:
The first picture has no transparency (alpha = 1), while the second has about alpha=0.6. As can be seen, in the second, specular reflections show up, which are clearly the specular colors of the hidden/rear side of the green double ball. I do not want this ‘double specularity’. How do I limit specular to only the ‘front’ surfaces?
Oh, and no raytracing is used, just standard rendering with buffer shadows.
in the top picture, the ball on the left is semi-transparent. I know because I can see the edge of the right ball inside of it. that is why you get that specular flare inside of it. the other two white spots in the middle of the balls is the specular from the front (outside) of the ball. In the bottom picture, the backside inside of a transparent ball will reflect colors; that’s they way nature is.
There is no ball on the left. The green one is a single mesh, two UVspheres spliced (cut away intersecting part, remove excess vertices). There are no transparencies at all in the top picture.
And that the inside will always provide specularity, wanted or not, seems implausible to me. Every 3D program I know leaves it as a choice to the user whether or not the reverse face of a polygon (the actual face being decided by the direction of the normals) is visible. Heck, in most other programs I know, the default is that an object’s mesh is not visible if viewed from the ‘wrong’ side. There has to be a way to make mesh polygons ‘onesided’ in Blender, too.
EDIT: No worries, I got it! Mesh, “No V.Normal Flip” must be on. ‘Backface culling’ was the term I was looking for. I must be getting old…
